使用 MyBatis 实现基本的 CRUD 操作

MyBatis 是一个优秀的持久层框架，它通过 XML 或注解将 SQL 查询、存储过程以及 Java 对象关联起来，简化了数据持久层的开发。本文将详细介绍如何使用 MyBatis 实现基本的 CRUD（Create、Read、Update、Delete）操作。

1. 环境准备

在开始之前，请确保已安装以下环境和工具：

JDK 8 或更高版本
Maven
MySQL 数据库（或其他数据库）
MyBatis 框架

1.1 创建数据库和表

首先，我们需要创建一个数据库和相应的表。在 MySQL 中执行以下 SQL 语句：

CREATE DATABASE mybatis_demo;USE mybatis_demo;CREATE TABLE users (id INT AUTO_INCREMENT PRIMARY KEY,name VARCHAR(50),email VARCHAR(50)
);

1.2 创建 Maven 项目

创建一个新的 Maven 项目，并在 pom.xml 中添加以下依赖：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.example</groupId><artifactId>mybatis-demo</artifactId><version>1.0-SNAPSHOT</version><dependencies><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.9</version></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.23</version></dependency><dependency><groupId>org.mybatis</groupId><artifactId>mybatis-spring</artifactId><version>2.0.6</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-context</artifactId><version>5.3.5</version></dependency></dependencies>
</project>

2. 配置 MyBatis

2.1 MyBatis 配置文件

在 src/main/resources 目录下创建 mybatis-config.xml 配置文件：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><settings><setting name="logImpl" value="STDOUT_LOGGING"/></settings>
</configuration>

2.2 MyBatis 映射文件

在 src/main/resources 目录下创建 UserMapper.xml 文件：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.mybatisdemo.mapper.UserMapper"><resultMap id="UserResultMap" type="com.example.mybatisdemo.model.User"><id property="id" column="id" /><result property="name" column="name" /><result property="email" column="email" /></resultMap><select id="selectUser" resultMap="UserResultMap">SELECT * FROM users WHERE id = #{id}</select><insert id="insertUser" parameterType="com.example.mybatisdemo.model.User">INSERT INTO users (name, email) VALUES (#{name}, #{email})</insert><update id="updateUser" parameterType="com.example.mybatisdemo.model.User">UPDATE users SET name = #{name}, email = #{email} WHERE id = #{id}</update><delete id="deleteUser" parameterType="int">DELETE FROM users WHERE id = #{id}</delete>
</mapper>

3. 创建实体类和接口

3.1 创建 User 实体类

在 src/main/java/com/example/mybatisdemo/model 目录下创建 User.java 文件：

package com.example.mybatisdemo.model;public class User {private int id;private String name;private String email;// Getters and Setterspublic int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}@Overridepublic String toString() {return "User{id=" + id + ", name='" + name + '\'' + ", email='" + email + '\'' + '}';}
}

3.2 创建 UserMapper 接口

在 src/main/java/com/example/mybatisdemo/mapper 目录下创建 UserMapper.java 文件：

package com.example.mybatisdemo.mapper;import com.example.mybatisdemo.model.User;
import org.apache.ibatis.annotations.*;@Mapper
public interface UserMapper {@Select("SELECT * FROM users WHERE id = #{id}")User selectUser(int id);@Insert("INSERT INTO users(name, email) VALUES(#{name}, #{email})")@Options(useGeneratedKeys = true, keyProperty = "id")void insertUser(User user);@Update("UPDATE users SET name=#{name}, email=#{email} WHERE id=#{id}")void updateUser(User user);@Delete("DELETE FROM users WHERE id=#{id}")void deleteUser(int id);
}

4. 配置 Spring 和 MyBatis

4.1 Spring 配置文件

在 src/main/resources 目录下创建 applicationContext.xml 文件：

<?xml version="1.0" encoding="UTF-8" ?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:context="http://www.springframework.org/schema/context"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/contexthttp://www.springframework.org/schema/context/spring-context.xsd"><context:component-scan base-package="com.example.mybatisdemo"/><bean id="dataSource" class="org.apache.commons.dbcp2.BasicDataSource"><property name="driverClassName" value="com.mysql.cj.jdbc.Driver"/><property name="url" value="jdbc:mysql://localhost:3306/mybatis_demo?useSSL=false&amp;serverTimezone=UTC"/><property name="username" value="root"/><property name="password" value="password"/></bean><bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"><property name="dataSource" ref="dataSource"/><property name="mapperLocations" value="classpath:com/example/mybatisdemo/mapper/*.xml"/></bean><bean class="org.mybatis.spring.mapper.MapperScannerConfigurer"><property name="basePackage" value="com.example.mybatisdemo.mapper"/></bean>
</beans>

5. 编写测试类

在 src/main/java/com/example/mybatisdemo 目录下创建 Main.java 文件：

package com.example.mybatisdemo;import com.example.mybatisdemo.mapper.UserMapper;
import com.example.mybatisdemo.model.User;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class Main {public static void main(String[] args) {ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");UserMapper userMapper = context.getBean(UserMapper.class);// CreateUser newUser = new User();newUser.setName("John Doe");newUser.setEmail("john.doe@example.com");userMapper.insertUser(newUser);System.out.println("Inserted: " + newUser);// ReadUser user = userMapper.selectUser(newUser.getId());System.out.println("Selected: " + user);// Updateuser.setName("Jane Doe");user.setEmail("jane.doe@example.com");userMapper.updateUser(user);System.out.println("Updated: " + user);// DeleteuserMapper.deleteUser(user.getId());System.out.println("Deleted user with ID: " + user.getId());}
}